Glycerol molecule provides three sites for combining with fatty acids to make ester products. Common oils and fats are triesters of glycerol called triacylglycerols, mono- and diacylglycerols are partial glycerol esters that are being increasingly used as emulsifiers in both foods and pharmaceuticals. Currently there is a growing need to make tri- and diacylglycerols that contain specific nutritionally important fatty acids at specified positions on the three-pronged glycerol backbone.
Diacylglycerols are widely used in a variety of applications such as additives for improving plasticity of oils and fats, as well as edible oils in the food industry, and as a base material for the production of cosmetics, drugs, etc. Generally, the preparation of such diacylglycerols involves an esterification reaction of glycerol with its corresponding fatty acid, an alcohol interchange reaction of glycerol with oil or fat, or the like, with the use of an alkali catalyst, or an enzyme such as a lipase, or the like. The use of an enzyme catalyst has been claimed to be the preferable choice, as compared to the chemical reaction process, from the viewpoints of the yield and purity of the diacylglycerols synthesized and energy savings. However, this is only true if the chemical reaction processes make use of conventional alkali catalyst, high reaction temperature and pressure.
Japanese Patent Application No. 71495/1989 discloses lipase-catalysed reaction processes in which a fatty acid or the like is reacted with glycerol in the presence of a 1,3-position selective lipase while removing water formed by the reaction outside the system, to obtain a diacylglycerol at high yield and purity. PCT Patent Application No. WO 99/09119 by Kao Corporation discloses a process for producing high-purity diacylglycerols at a low cost and more efficiently than conventional esterification and glycerolysis processes, which comprises partially hydrolyzing an oil or fat, followed by esterifying the resultant product with glycerol. Japanese Patent Application No. 234391/1998 discloses processes in which a mixture of a fatty acid or the like and glycerol or the like is reacted in a flow tube type reactor filled with a lipase while controlling the superficial velocity of the mixture in the reactor to at least 0.05 cm/s. Japanese Patent Application No. 330289/1992 discloses processes in which glycerol is added in an equimolar amount or more to a fatty acid to react, the reaction is stopped when the concentration of a diacylglycerol has been enhanced, insoluble glycerol is separated, and the reaction is further conducted while dehydrating, thereby synthesizing diacylglycerol at a high esterification reaction rate by improving dehydration efficiency. U.S. Pat. No. 6,361,980 discloses a process for preparing a diacylglycerol, comprising: an enzyme-packed tower comprising an immobilized lipase preparation, carrying out an esterification reaction between: (1) an acyl group donor selected from the group consisting of a fatty acid, a lower alcohol ester thereof, and a mixture thereof; and (2) an acyl group acceptor selected from the group consisting of glycerol, a monoacylglycerol, and a mixture thereof; to obtain a reaction fluid from said enzyme-packed tower; reducing a water content or a lower alcohol content in said reaction fluid; and subsequent to said reducing, re-circulating the reaction fluid to said enzyme-packed tower, wherein a residence time of said reaction fluid in said enzyme-packed tower is 120 seconds or less; to obtain a diacylglycerol, wherein said reducing comprises dehydrating or de-alcoholising said reaction fluid is by feeding said reaction fluid though a spray nozzle, in a dehydration process. United States Patent Application No. 2003/0104109 discloses a method for producing 1,3-diacylglycerol oil from triacylglycerol, comprising mixing the triacylglycerol containing oil with glycerol and a homogenous chemical catalyst comprising an alkali metal salt or alkali earth metal salt of a monocarboxylic acid or a dicarboxylic acid, or a mixture thereof, to achieve glycerolysis, wherein the 1,3-diacylglycerol oil is produced.
Among the above-described processes, however, the technique disclosed in Japanese Patent Application No. 71495/1989, PCT Patent Application No. WO 99/09119, Japanese Patent Application No. 234391/1998, Japanese Patent Application No. 330289/1992 and U.S. Pat. No. 6,361,980, make use of expensive lipases as catalyst for the reaction, and therefore, are difficult to produce diacylglycerol at a low cost; the technique disclosed in Japanese Patent Application No. 330289/1992 involves technical difficulties such as the necessity of stopping the reaction at a specific time when the concentration of diacylglycerol reaches a peak; the technique disclosed in Japanese Patent Application No. 234391/1998 could not obtain sufficient purity of diacylglycerol; the technique disclosed in United States Patent Application No. 2003/0104109 requires an immediate removal of the homogenous chemical catalyst after the reaction by means of neutralization, which is not easy to operate at an industrial level and may lead to diacylglycerol oil loss.
Obesity is a well-known lifestyle disease that is widespread in affluent nations and rapidly on the rise in developing countries. It is often related to many diseases such as diabetes, hyperlipemia, hypertension and ischemic heart diseases. One of the reasons of the onset of obesity lies in the excessive intake of fat in our daily diet, which results in the increased accumulation of body fat.
In view of this situation, numerous fat substitutes or low-calorie fats have been developed to replace or reduce the use of conventional fats. Examples of such fats include sucrose fatty acid esters, alkyl glycoside fatty acid polyesters, dialkyl dihexadecylmolonate, esterified propoxylated glycerol and long-chain and short-chain fatty acids of triacylglycerols. However, such fats do not satisfy important characteristics such as nutritional safety, desirable physical property, heat stability, and flavour; all of which are critical for the fat to be acceptable by consumers. Medium-chain and long-chain fatty acid triacylglycerols have been shown to satisfy all of the above criteria and to lower body fat accumulation, and the production is therefore desirable.
United States Patent Application No. US2004/0191391 discloses a lipase-catalysed reaction process in which an edible oil or fat is transesterified or acidolysed with medium-chain fatty acids or medium-chain fatty acids triacylglycerol. This process makes use of expensive lipases as catalyst for the reaction, and therefore, is difficult to produce medium-chain and long-chain fatty acids triacylglycerol at a low cost.
European Patent Application No. EP1642959 discloses a 3-stage process for preparing high purity symmetrical triacylglycerols comprising of medium-chain fatty acids at sn-1 and sn-3 positions and a long-chain fatty acid at sn-2 position in which, (1) a medium-chain fatty acid triacylglycerol is randomly transesterified with a long-chain fatty acid triacylglycerol in the presence of an enzyme or a chemical catalyst to obtain a reaction product containing a triacylglycerol comprising a medium-chain fatty acid and a long-chain fatty acid, (2) reaction product from (1) is transesterified with an alcohol monoester of a medium-chain fatty acid in the presence of a 1,3-position specific enzyme, and (3) separating the alcohol monoester of the medium-chain fatty acid and the alcohol monoester of the long-chain fatty acid monoester to obtain the symmetrical triacylglycerol composing of medium-chain fatty acids at the sn-1 and sn-3 positions and a long-chain fatty acid at the sn-2 position. This process also makes use of expensive lipases as catalyst and alcohol monoesters of medium-chain fatty acids as raw materials for the transesterification reaction, and therefore, makes the process difficult to produce medium-chain and long-chain fatty acid triacylglycerols at a low cost.
United States Patent Application No. US2004/0171127 discloses a process for producing medium-chain and long-chain fatty acid triacylglycerol comprising of medium-chain fatty acids esterified to the sn-1 and sn-3 positions and a ω-6 series polyunsaturated long-chain fatty acid having 18 or more carbon atoms and 2 or more double bonds, but not containing ω-3 series polyunsaturated fatty acid, esterified to the sn-2 position of the triacylglycerol molecule, by means of enzymatic transesterification of medium-chain fatty acids and an oil or fat containing at least one polyunsaturated fatty acid of the abovementioned type, using an immobilized lipase. Similarly, this process also involves the use of expensive lipases as catalyst, and therefore, increases the overall production cost of medium-chain and long-chain fatty acid triacylglycerols.
In view of the above, it is advantageous to provide a method of producing fats and oil containing acylglycerol esters. This method would be desirable to produce diacylglycerols and/or medium-chain and long-chain fatty acid triacyglycerols at a high yield and low cost in a short period of time, which has potential applications in the continuous commercial production of diacylglycerols and/or triacylglycerols having medium-chain and long-chain fatty acids at industrial level.